Sheet necking prediction in forming limit diagrams with the anisotropy influence incorporation

Abstract

A well-known method of materials formability description is the Forming Limit Diagram (FLD). In FLDs/FLC (Forming Limit Curve) a plot of major and minor principal strains in the plane of deformed sheet where necking takes place is represented. The current paper is dealing with anisotropy influence on FLC. This effect is going to be studied with the use of mild steel DC01. Hills anisotropic criterion is considered here and for its application experimental investigation has to be carried out in order to provide input data for the model applied. Uniaxial tensile tests were performed for basic characterisation of sheet samples with the use of contact-less measuring devices. In order to assess the anisotropy experimentally, the specimens were extracted and tested in Rolling Direction (RD), Transverse Direction (TD) and 45° Skew Direction (SD) for the Lankford ratios determination. Detailed stress state description of the material investigated was carried out with the use the stress triaxiality and Lode angle parameter. Therefore, transformations from conventional space into stress state provide a profound insight into the necking phenomenon. According to the experimental and numerical results it was found that it is necessary to take anisotropy effects into account for the material investigated.